The term stent generally refers to a prosthesis, which can be introduced into a corporeal lumen and expanded to support that lumen or attach a conduit to the inner surface of that lumen.
A number of prior art references are available in the art, each of which references are directed to some specific discreet elements of the system which are described and claimed in the present invention, however, none of which is directed to the totality of the combination, or its use and function in the manner described and claimed herein.
The following prior art references are known to the inventor:
U.S. Pat. No. 4,580,568, which issued to Gianturco on Apr. 8, 1986, discloses an endovascular stent formed of stainless steel wire which is arranged in a closed zig-zag pattern;
U.S. Pat. No. 4,733,665, which issued to Palmaz on Mar. 29, 1988, relates to an expandable intraluminal vascular graft which is expanded within a blood vessel using an angioplasty balloon associated with a catheter;
U.S. Pat. No. 4,739,762, which issued to Palmaz on Apr. 26, 1988, teaches an expandable intraluminal graft for use within a body passageway or duct which is particularly useful for repairing blood vessels which have been narrowed or occluded by disease;
U.S. Pat. No. 4,830,003, which issued to Wolff et al on May 16, 1989, discloses a cylindrical shaped stent useful to prevent arterial acute closure which is formed of longitudinal wires of biocompatible material which wires have been welded together in pairs at alternate ends with each pair or wires bent into a V-section. The wires are formed into a cylinder which is welded closed in order to form the stent;
U.S. Pat. No. 5,104,404, which issued to Wolff on Apr. 14, 1992, teaches an intravascular stent which is applied within the peripheral or coronary arteries of a living animal or a human being in order to return patency after a balloon angioplasty. The stent taught in this reference is an articulated separate stent comprising at least two segments each of which segments have a generally tubular shape and a hinge means extending between and connecting adjoining stent segments;
U.S. Pat. No. 5,019,090, which issued to Pinchuk on May 28, 1991, relates to radially expandable stents which include a plurality of adjacent generally circumferential sections which are substantially axially positioned with respect to each other;
U.S. Pat. No. 4,886,062, which issued to Wiktor on Dec. 12, 1989, discloses a device which is to be used as a vascular stent comprising a cylindrical open ended wire made of a low memory metal, which is characterized by its ability to be expanded radially to a larger diameter after initial implantation, along with a means for causing said stent to expand to a larger diameter and a method for transporting, positioning and implantation of such stent;
U.S. Pat. No. 5,370,683, which issued to Fontaine on Dec. 6, 1994, is directed to a vascular stent for reducing hemodynamic disturbances caused by angioplasty, said stent being formed from a single filament of low memory biocompatible material having a series of U-shaped bends. The filament is wrapped about a mandril in a circular fashion in order to align the curved portions of each bend which may then be connected;
U.S. Pat. No. 5,226,913, which issued to Pinchuk on Jul. 13, 1993, teaches a radially expandable stent which includes a plurality of adjacent generally circumferential sections that are substantially axially positioned with respect to each other, wherein at least one of the generally circumferential sections has an expandable segment which imparts a circumferential and radial expandablility to the stent;
U.S. Pat. No. 4,913,141, which issued to Hillstead on Apr. 3, 1990, relates to a stent delivery system for routing the stent to a defined position within a subject""s blood vessel;
U.S. Pat. No. 5,133,732, which issued to Wiktor on Jul. 28, 1992, discloses a stent for implantation into a body vessel comprising a cylindrical stent body which has been coiled from a generally continuous wire which has been imparted with a deformable zig-zag structure;
U.S. Pat. No. 5,135,536, which issued to Hillstead on Aug. 4, 1994, is directed to a stent for reinforcing a vessel wall which is constructed from a single elongated wire. The wire has been first bent into a series of tight bends and then rolled around a mandrel in order to create junctions of wire which are permanently adhered. The completed stent forms cylindrical shape which can be expanded from its initial diameter to a larger implanted diameter by the application of radial outward force from a balloon catheter;
U.S. Pat. No. 4,655,771, which issued to Wallsten on Apr. 7, 1987, teaches a prosthesis for transluminal implantation comprising a flexible tubular body which has a diameter that is variable by axial movement of the ends of the body relative to each other and which is composed of several individual rigid but flexible thread elements each of which extends in helix configuration with the centerline of the body as a common axis;
U.S. Pat. No. 5,015,253, which issued to MacGregor on May 14, 1991, discloses a generally tubular stent that includes a non-woven structure formed by two or more generally helically shaped cylinders of stiff strand material where the strand material forming the non-woven structure is preferably secured together at attachment sites which allow the stent to be flexible and adjustable to meet various needs.
Most manifestations of the available prior art expand by the rotation of a structural element (limb) from a longitudinal orientation (parallel to the long axis of the stent) to a more transverse orientation. The limbs themselves change very little in shape. Stents, in which adjacent limbs are linked to form rings, spirals, or a series of linked rings, expand and contract by deformation of the structural elements in the immediate vicinity of the junction between limbs. In the case of self-expanding stents, the junctions serve as reservoirs of energy, which produce stent expansion. However, the isolation of mechanical stress to such small portions of the stent limits the expansion ratio and renders the stent less durable.
An example of this effect is the Gianturco Z-stent (""568). This stent is comprised of a single loop of wire, in which alternating straight segments wind back and forth between bends to form a crown. In the Ginaturco Z-stent the junctional stresses can be diffused by increasing the radius of curvature at the bends; the larger the bend the more diffuse the stress. However, large radius bends limit the expansion ratio, because the bends take up more space than straight segments. Bending the limbs themselves does little to reduce the stress, because these bends are much less amenable to deformation than the bends between adjacent limbs. When the stent is compressed, the limbs soon meet along the outer curvatures of any bends. Any attempt to further collapse the stent by straightening the limbs is thwarted by the overlapping.
Other stents, which have no rings or spirals of alternating limbs and no fixed junctions between limbs are free of these problems, however, they also lack the expansile energy provided by junctional deformation, and therefore, tend to expand rather weakly. There are currently no self-expanding stents available in the prior art in which the relative positions of the joined limbs change as a result of deformation that is distributed over large segments of the limbs.
It is, therefore, an object of the present invention to provide for an improved stent which exhibits superior expansion characteristics over available prior art stents.
It is a further object of the present invention to provide for an improved stent in which the limb elements have been fabricated from a medium having a cross sectional profile in which at least one segment is flat and straight, which exhibits superior expansion characteristics over available prior art stents.
Lastly, it is an object of the present invention to provide for an improved stent which exhibits superior expansion characteristics over available prior art stents while at the same time avoiding the compression and deformation problems associated with other prior art stents.
These and other objects of the invention will become apparent from the following discussion of the invention.
The present invention provides for an improved stent in which the limbs have been fabricated from a medium having a cross sectional profile in which at least one segment is straight, whereby the stent is provided with improved expansion characteristics.